Vertical preloader

i want to create a preloader with a bar that fills up vertically, from bottom to top. i have this basic preloader code:

bytes_loaded = Math.round(this.getBytesLoaded());
bytes_total = Math.round(this.getBytesTotal());
getPercent = bytes_loaded/bytes_total;
this.loadBar._width = getPercent175;
this.loadText = Math.round(getPercent
if (bytes_loaded == bytes_total) {

loadBar is the preloader-bar movie clip.
just changing “width” to “height” doesn’t do the trick - it’s vertical but starts from the centre and expands on both ends, and then goes much further then it really should.

what do i need to change? is this much more complicated then creating the horizontal bar?